1. Field of the Invention
The invention relates to a method for improving data accuracy in an optical disc drive, and particularly to a method having a plurality of read procedures to read data on an optical disk depending in what a read mode the optical disc drive is.
2. Description of the Related Art
Recently, optical storage media, such as compact disc (CD) and recordable compact disc (CD-R and CD-RW) has had significant advance in the evolution of data storage. With the development of optical storage media, data can be recorded and backed up into optical disks with high capacity and light weight. Furthermore, the optical storage media has superior and reliable quality for audio and video data. As an obvious result, the optical storage media has been replacing a lot of traditional data storage media, such as tapes and films.
FIG. 1 shows a block diagram of a disc servo system in an optical disc drive as an example. An optical head 11 reads reflected signals from an optical disc 10. Being amplified and processed by the RF (Radio Frequency) IC 12, the FE (Focus Error) signal, TE (Track Error) signal and relative data and signals as read are input to DSP (Digital Signal Processor) and microprocessor 13.
After analyzing the received signals, the microprocessor 13 accordingly generates and outputs signals to corresponding servos (Focusing Servo 14, Tracking Servo 15 and Spindle Motor Servo 16) to control the actuators (focusing actuator 17 and tracking actuator 18), sled motor 19 and spindle motor 20 and to ensure data accuracy during reading or writing.
Damaged tracks on the optical disc and defocus of the laser beam from the optical head 11 occur from time to time. These events cause readout data from the optical disk as inaccurate or unacceptable. Since these events is inevitable and readout data should be as accurate as possible, there is a need to improve data accuracy while read data on the optical disk.
Traditionally, the method for improving data accuracy is to reread the data while the data as read is unacceptable no matter what kind of a read mode the disk servo system is in. Details of the traditional method are shown in FIG. 2. First, the optical head of the optical disc drive reads data from an optical disc (step S1). When the data cannot be read (or is unacceptable as read) and a buffer for temporarily storing readout data stores an sufficient amount of data for output (step S2), the data is reread (step S1). The sufficient amount is in consideration of smoothness of data follow in view of the data receiver, receiving data from the buffer, to prevent from any discontinuity of the data follow. When the data is read correctly (in other words, acceptable) or the buffer has an insufficient amount of data for output, the data is compulsorily written into the buffer (step S3). Eventually, the data is output (step S4) form the buffer.
Generally, if the disc servo system is in a document read mode (reading documentary files from an optical disk), data accuracy is the most important consideration and rereading the disc may be executed as many times as wished. Nevertheless, when the disc servo system is in an audio/video play mode (playing an audio/video program from an optical disk), not only the data accuracy but also time constrain must be considered. Data accuracy provides high quality of sound or picture can be achieved or enhanced by rereading, as mentioned before. But, human being is also sensitive to any break or discontinuity while enjoying an audio/video program. When rereading is executed too many times, output of data from the buffer may be interrupted and break or discontinuity in data flow occurs because of running out of the data inside the buffer. In other words, compromise between data accuracy and time constrain is necessary and inevitable when the disc servo is in an audio/video mode.
Following the method in FIG. 2, the traditional disk servo system has only one criteria to decide whether rereading is executed. If this criteria is set for guaranteeing data accuracy, too many times of rereading may occur and an user will hear or see break/noise while the disk servo system is playing an audio/video program. If this criteria is set for guaranteeing smoothness of data flow, unacceptable or erroneous data may be output to cause a defective document while the disk servo system is reading a file for copy. One criteria beneficial to performance in one read mode will damage performance in the other read mode.